Mars appears to be deficient in large craters relative to Mercury and the Moon. This relative deficiency conflicts with the interpretation of a common population of impactors within the early inner solar system and suggest either of two possibilities. If the apparent deficiency of martian craters is real then the population of impactors at Mars differed significantly from that closer to the Sun. If the apparent deficiency is not real then the complete crater inventory of Mars should be similar to those of Mercury and the Moon, supporting the interpretation of a single population of impactors. These alternate possibilities can be tested by comparing revised inventories that include partly buried or eroded craters to an estimate of Mars' possible relative crater deficiency.